Jackson removed the 'Aragorn vs Sauron' fight because using fourteen-foot bad guys in suits of armour as the climax for an entire epic trilogy just didn't work very well. He didn't remove that sequence out of a sense of loyalty to Tolkien – if that was the reason, it never would have made it past the storyboards. Once the battle had been filmed and intercut with the Cracks of Doom sequence, the filmmakers saw that it simply wasn't working very well, so they digitally replaced Sauron with a mountain troll.